Hindfoot valgus refers to malalignment of the hindfoot in which the mid-calcaneal axis is deviated away from the midline of the body.
Despite abduction of the calcaneus, the mid-calcaneal line does not significantly alter, and in some cases may intersect the metatarsal bases more medially than normally, e.g intersecting the base of the 3rd metatarsal rather than the base of the 4th.
This may seem counter-intuitive and certainly causes confusion.
The widening of the talocalaneal angle results in the apparent medial angulation of the mid-talar axis such that the line extends well medial to the base of the first metatarsal suggesting that the talus is medially angulated.
In fact, the talus is in the correct position (it has no muscular attachments) and it is the rest of the foot that is incorrectly positioned. The entire foot, under and distal to the talus has been abducted and everted. If the navicular is ossified, it will be laterally displaced.
Since the calcaneus is abducted, the talus loses support of its medial border and the distal portion of the talus drops, leading to a more vertically oriented talus and the mid-talar line on the lateral view does not intersect the 1st metatarsal.